CONSTRUCTED FLUID SYSTEMS SECTION 9.2

Objectives By the end of the lesson you will be able to: 1. Explain the difference between static and dynamic pressure 2. Describe and give examples of hydraulic and pneumatic systems 3. Use pressure to explain different problems in hydraulic and pneumatic systems

FLUIDS AT REST enclosed Remember Pascal?  also observed when pressure is applied at one point to a fluid in an enclosed system, that pressure is transmitted equally through the entire system Ex: squeezing a tube of toothpaste from the bottom of the tube forces paste out at the top (if the lid is off!)

Fluids at Rest Squeezing an enclosed fluid creates static pressure = the fluid is able to apply a force even though it is not moving (static = not moving) Ex: pressing the brakes in a car compresses the fluid in the brake lines causing brake pads to push against the wheels = FRICTION! And the car stops!

How Brakes Work Turn to page 325 to see a great picture of how they work. Explain how it works in your own words.

Fluids in Motion Fluid in motion has dynamic pressure Can use this energy to perform tasks – ex: spraying water out of a hose Bernoulli (Swiss scientist) observed that as the speed of a fluid increases, the pressure exerted perpendicular to the motion decreases Ex: air travels faster over the top of an airplane wing creating an area of low pressure above the wing = greater pressure under the wing pushes the plane upwards

Hydraulic Systems Hydraulics = study of pressure in liquids Hydraulic systems = devices that create pressure that moves through a liquid like oil or water Liquids are NOT compressible under typical pressures When there is continuous pressure applied to a liquid enclosed in a pipe or tube, the force is transmitted along the liquid You can apply pressure to water in a pipe in one location and the force could perform a task in another location  see example next slide

Example of hydraulic system -The force of the water spraying out of the hose is due to the pressure applied to water in a pipe many miles away

Hydraulic Fluid Transportation Pumps = important parts of hydraulic systems  used to raise or move fluids  work to create areas of low and high pressure to move water along a pipe One example of a hydraulic system = water into your house from a well Works with a pump which forces water through a pipe into a pressure tank  more and more water enters the tank causing the air pressure inside to increase  when enough pressure occurs, tank sends an electrical signal to turn the pump off and the tank transmits water under pressure through the system

Valves Valves = another part of hydraulic systems Device for controlling the passage of fluid through a pipe When closed = stops flow of water When opened = allows flow of water Check valves = valves that allow fluids to flow in only one direction  Real life example = heart valves!

Hydraulic Multiplication Hydraulic systems can also multiply the force exerted by a liquid Hydraulic multiplication = an incompressible fluid increases and transmits a force from one point to another Ex: hoisting vehicles for repair htm htm

Problems in Hydraulic Systems Twists and turns in pipe systems increase resistance to flow Bad pipe connections can cause leaking Pressure in a system is affected by the size of the pipe and how smooth the insides of the pipes are  Fluid particles lose energy as they brush past each other in confined spaces and as they bump into the walls of the pipelines Build-up of sludge, corrosion and mineral deposits all interfere with water flow

Problems in Hydraulic Systems Example: imagine using a very small straw or a very big/ wide straw. -Which straw would be easiest to use to drink the shake?

Pneumatic Systems Pneumatics = use of gas (usually air) in an enclosed system under pressure Similar to hydraulic systems except gases are used instead of liquids An enclosed gas transmits a force causing motion Works because gases can be compressed Uses a compressor so air pressure builds up; as pressure is released air particles move apart suddenly creating a strong and steady force for a short time to perform powerful tasks Examples of tools using pneumatics: tampers (pack down dirt and gravel) and dentist drills

Pneumatic Systems Can also be used with hydraulic multiplication  heavy trucks and buses use pneumatic brakes because they need a larger force to stop - (comes from compressed air)

Problems in Pneumatic Systems Do not work well if movement of gas is blocked Read the example on page 331 and summarize in your own words what can happen if the movement of gas is blocked